Using my own key in an AES encryption algorithm implementation - encryption

Question

I have the following code:
import java.security.SecureRandom;
import javax.crypto.Cipher;
import javax.crypto.KeyGenerator;
import javax.crypto.SecretKey;
import javax.crypto.spec.SecretKeySpec;
public class AESHelper {
public static String encrypt(String seed, String cleartext) throws Exception {
byte[] rawKey = getRawKey(seed.getBytes());
byte[] result = encrypt(rawKey, cleartext.getBytes());
return toHex(result);
}
public static String decrypt(String seed, String encrypted) throws Exception {
byte[] rawKey = getRawKey(seed.getBytes());
byte[] enc = toByte(encrypted);
byte[] result = decrypt(rawKey, enc);
return new String(result);
}
private static byte[] getRawKey(byte[] seed) throws Exception {
KeyGenerator kgen = KeyGenerator.getInstance("AES");
SecureRandom sr = SecureRandom.getInstance("SHA1PRNG");
sr.setSeed(seed);
kgen.init(128, sr); // 192 and 256 bits may not be available
SecretKey skey = kgen.generateKey();
byte[] raw = skey.getEncoded();
return raw;
}
private static byte[] encrypt(byte[] raw, byte[] clear) throws Exception {
SecretKeySpec skeySpec = new SecretKeySpec(raw, "AES");
Cipher cipher = Cipher.getInstance("AES/ECB/PKCS5Padding");
cipher.init(Cipher.ENCRYPT_MODE, skeySpec);
byte[] encrypted = cipher.doFinal(clear);
return encrypted;
}
private static byte[] decrypt(byte[] raw, byte[] encrypted) throws Exception {
SecretKeySpec skeySpec = new SecretKeySpec(raw, "AES");
Cipher cipher = Cipher.getInstance("AES/ECB/PKCS5Padding");
cipher.init(Cipher.DECRYPT_MODE, skeySpec);
byte[] decrypted = cipher.doFinal(encrypted);
return decrypted;
}
public static String toHex(String txt) {
return toHex(txt.getBytes());
}
public static String fromHex(String hex) {
return new String(toByte(hex));
}
public static byte[] toByte(String hexString) {
int len = hexString.length()/2;
byte[] result = new byte[len];
for (int i = 0; i < len; i++)
result[i] = Integer.valueOf(hexString.substring(2*i, 2*i+2), 16).byteValue();
return result;
}
public static String toHex(byte[] buf) {
if (buf == null)
return "";
StringBuffer result = new StringBuffer(2*buf.length);
for (int i = 0; i < buf.length; i++) {
appendHex(result, buf[i]);
}
return result.toString();
}
private final static String HEX = "0123456789ABCDEF";
private static void appendHex(StringBuffer sb, byte b) {
sb.append(HEX.charAt((b>>4)&0x0f)).append(HEX.charAt(b&0x0f));
}
}
and the main class:
public class MainActivity extends Activity {
String seedValue = "This Is MySecure";
#Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
String normalText = "VIJAY";
String normalTextEnc;
try{
normalTextEnc = AESHelper.encrypt(seedValue, normalText);
String normalTextDec = AESHelper.decrypt(seedValue, normalTextEnc);
TextView txe = new TextView(this);
txe.setTextSize(14);
txe.setText("Normal Text ::" + normalText + " \n Encrypted Value :: " + normalTextEnc + " \n Decrypted value :: " + normalTextDec);
setContentView(txe);
}catch(Exception e){
// TODO Auto-generated catch block
e.printStackTrace();
}
}
}
How can I use my own key?
What is the use of a rawKey?

Answer 1

That's the getRawKey function I've been fighting against for as long as I'm on StackOverflow. To use a password, use PBKDF2, it's build into Java. To create a random key, use a random number generator new SecureRandom() and SecretKeySpec.
If your random number generator ever does anything unexpected, e.g. generating a random number instead of acting as a deterministic PRNG your key will not be the same and you may never decrypt your ciphertext again. This actually happened after an update on Android where the default provider was replaced and the RNG differed from the one before.

Answer 2

package com.example.encryption;
import javax.crypto.Cipher;
import javax.crypto.SecretKey;
import javax.crypto.spec.SecretKeySpec;
import java.util.Base64;
public class AESOwnKey {
private Cipher ecipher;
private Cipher dcipher;
AESOwnKey(SecretKey key) {
try {
ecipher = Cipher.getInstance("AES");
dcipher = Cipher.getInstance("AES");
ecipher.init(Cipher.ENCRYPT_MODE, key);
dcipher.init(Cipher.DECRYPT_MODE, key);
} catch (Exception e) {
System.out.println("Failed in initialization");
}
}
public byte[] encrypt(String str) {
try {
byte[] utf8 = str.getBytes("UTF-8");
byte[] enc = ecipher.doFinal(utf8);
return Base64.getEncoder().encode(enc);
} catch (Exception e) {
System.out.println("Failed in Encryption");
}
return null;
}
public String decrypt(byte[] bytes) {
try {
byte[] dec = Base64.getDecoder().decode(bytes);
byte[] utf8 = dcipher.doFinal(dec);
return new String(utf8, "UTF-8");
} catch (Exception e) {
System.out.println("Failed in Decryption");
}
return null;
}
public static void main(String[] args) {
try {
String mykey = "1234567891234567";
SecretKey key = new SecretKeySpec(mykey.getBytes(), "AES");
AESOwnKey encrypter = new AESOwnKey(key);
String original = "Testing encryption";
System.out.println("Before Encryption : " + original);
byte[] encrypted = encrypter.encrypt(original);
System.out.println("After Encryption : " + encrypted);
String decrypted = encrypter.decrypt(encrypted);
System.out.println("After Decryption : " + decrypted);
} catch (Exception e) {
}
}
}